Inorganic microparticle powders such as microparticle titanium dioxide have been used for cosmetic materials such as sunblock in order to impart ultraviolet blocking performance in the related art.
However, when inorganic microparticle powders are mixed in the form of a powder into cosmetic materials, it is impossible to sufficiently disperse the powders with a common stirring means such as a homogenizer, a disperser and an emulsifying machine due to strong aggregation force between powders. For this reason, transparency of cosmetic materials is deteriorated, and as a result, in some cases, unnatural whitening occurs or, SPF value, which is an ultraviolet blocking indicator, cannot be sufficiently secured.
Also, when inorganic microparticle powders are mixed into cosmetic materials in the form of powders, there are problems in which handling is difficult and additional dust countermeasures are required since inorganic microparticle powder has a small particular diameter.
In this regard, dispersion is generally carried out by using a disperser having a strong stirring force such as sand grinder mill in order to further prevent aggregation between powders, or by adding silicone-based dispersing agent such as polyether modified silicone or a surfactant in order to inhibit reaggregation after dispersion and maintain dispersion stability.
Also, incorporation of a liquid dispersion obtained by previously dispersing the inorganic microparticle powders in oils such as silicone oils, ester oils, liquid paraffin or decamethylcyclopentasiloxane into cosmetic materials is carried out.
Specifically, PTL 1 discloses an oily dispersion obtained by defining an average particle diameter and a shape of microparticle titanium dioxide and using a specific organic dispersing agent, and PTL 2 discloses a method for preparing a coating composition of microparticle titanium dioxide wherein dispersion stability after dispersion is improved by adding an aluminum salt and fatty acid (salt) having 7 or more carbon atoms to an aqueous suspension of rutile-type microparticle titanium dioxide.
Further recently, microparticle titanium dioxide or oily dispersion that focuses on dispersibility of isostearic acid, for example, disclosed in PTLs 3 to 8 is developed.
Specifically, PTL 3 discloses an oily dispersion obtained by using isostearic acid and an oily solvent to a dispersion liquid of titanium alkoxide.
PTL 4 discloses microparticle titanium dioxide with superior ease of use, transparency and dispersibility by adding isostearic acid to an oily dispersion liquid and the like of titanium alkoxide, followed by coating.
PTL 5 discloses microparticle titanium dioxide in which ultraviolet protection performance can be further improved by adding isostearic acid to an oily dispersion liquid and the like of titanium alkoxide, dispersing, then removing the dispersion medium, and drying or baking.
PTL 6 discloses a microparticle titanium dioxide obtained by adding isostearic acid to an oily dispersion liquid or the like of titanium alkoxide, dispersing and then heating to the extent that the isostearic acid remains.
PTL 7 discloses an oily cosmetic material that has less aqueous stains and less stimulation in use obtained by containing microparticle titanium dioxide and isostearic acid.
PTL 8 discloses a cosmetic material slurry obtained by adding to isostearic acid and further adding polyether-modified methyl polysiloxane to microparticle titanium dioxide.